The present invention relates to a substrate, especially a transparent substrate, endowed with a property of hydrophobicity/oleophobicity for the purpose of obtaining certain anti-rain/anti-fouling effects or else the property of hydrophilicity/oleophilicity, or a photocatalytic characteristic, this being associated, respectively, with anti-misting/anti-frosting and also anti-staining effects, or with other properties: fragrance, etc. For this purpose, such a substrate, for example, is provided with a coating within the context of various applications, such as glazings for aeronautical, sea-going, land-borne (rail and road) transport vehicles, for building (windows), for urban furniture (display panels, bus shelters, etc.) or interior design (decorative panels, furnishings), domestic electrical appliances (refrigerator and oven doors, showcases, glass-ceramic plates), kitchen utensils, sanitaryware (washbasins, bathtubs, etc.), construction materials, etc.
The substrate is therefore transparent or non-transparent and consists, in general, of glass, ceramic, glass-ceramic, metal, plastic (polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polycarbonate (PC) or polyurethane (PU), thermoplastic ethylene/vinyl acetate copolymer (EVA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate/polyester copolymers, cycloolefin copolymers of the ethylene/norbornene or ethylene/cyclopentadiene type, ionomer resins, for example an ethylen/(meth)acrylic acid copolymer neutralized by a polyamine, thermosetting or thermally crosslinkable polymers such as polyurethane, unsaturated polyester (UPE), ethylene/vinyl acetate copolymer, etc.) or of a combination of several of these materials.
The hydrophobicity/oleophobicity property to which reference has been made means that polar or nonpolar liquids do not adhere to the substrate so as to form an annoying film. A substrate having this property will have little or almost no tendency to retain dust or dirt of any type, fingermarks, insects, etc.
The presence of water and/or dirt results in an unattractive appearance and, as the case may be, a reduction in the transparency of the substrate together with an impairment of vision through it. Water and dirt are particularly annoying when the substrate is used for glazing in the transportation field.
The property of hydrophobicity/oleophobicity, or non-wettability, of a substrate means that the contact angles between a liquid and this substrate are high, for example, at least 90xc2x0 in the case of water. The liquid therefore tends to flow off easily, in the form of drops, on the substrate simply under gravity if the substrate is inclined or due to the effect of aerodynamic forces in the case of a moving vehicle. Such known agents for imparting this hydrophobicity/oleophobicity property are, for example, fluoroalkylsilane such as those described in Patent Applications EP 0 492 417, EP 0 492 545 and EP 0 672 779.
Common hydrophobic/oleophobic agents are, in particular, alkyltrihalosilanes or alkyltrialkoxy-silanes, the alkyl group of which has at least one perfluorinated end group, that is to say one consisting of an F3Cxe2x80x94(CF2)nxe2x80x94 group in which n is a positive integer or zero, as described in Patent Application EP 0 719 743.
The hydrophobic/oleophobic agents are applied in a known manner as a solution using conventional deposition methods with or without heating.
One of the problems arising most acutely in the field of the invention is that of the durability of the hydrophobic/oleophobic coating. This is because durability is affected by the erosion which inevitably happens to some extent, for example during the periodically essential operations of cleaning the substrate when the latter is transparent, in order to restore satisfactory vision through the substrate. Thus, it is constantly endeavoured to slow down the rate of progressive removal of the hydrophobic/oleophobic coatings of the aforementioned types which takes place especially owing to the action of windscreen wipers, the more so as such removal may, in addition, result in degradation by ultraviolet radiation.
Two main approaches have hitherto been explored for increasing the durability of the coatings by limiting the erosion effects. Both these approaches consist in increasing the adhesion of the coatings to the substrates.
According to a first approach, Application EP 0 484 746 recommends the preparation of the substrate by a pre-treatment using a primer of the tetrahalosilane or tetralkoxysilane type.
Application EP 0 497 189 A2 proposes, according to a second approach, the prior creation on the surface of the substrate of irregularities having sizes, for example, of between 1 and 10 micrometers, either by adding particles or by various etching techniques such as chemical etching or sandblasting.
Moreover, it has been specified that, in all cases, there is no particular difficulty in reforming a new hydrophobic/oleophobic coating in order to remedy the erosion of the previous coating; this may be done on the old coating once it has been briefly cleaned. However, it is still obviously beneficial to delay this operation as long as possible.
The present invention is related to a substrate coated with a mesoporous film, wherein chemical molecules are bonded to the mesoporous film. In one embodiment, the substrate is made of a glass material or a plastic, and in another embodiment the substrate is made of glass. The mesoporous film may include at least one compound including at least one of the elements Si, W, Sb, Ti, Zr, Ta, V, Pb, Mg, Al, Mn, Co, Ni, Sn, Zn, In. The mesoporous film may have a periodic lattice on the scale of domains at least about 20 nm in size, and the mesoporous film may be electrically conducting. The chemical molecules may be hydrophobic/oleophobic and chosen from the group consisting of:
a) silicones; and
b) compounds satisfying the formulae: xe2x80x83and Rpxe2x80x2SiX4-pxe2x80x2xe2x80x83xe2x80x83(II)
xe2x80x83wherein m=0 to 15, n=1 to 5, p=0, 1 or 2, R is a linear or branched alkyl group or a hydrogen atom, X is a hydrolysable group such a halogen, alkoxy, acetoxy, acyloxy, amino or NCO group, and pxe2x80x2=0, 1, 2 or 3.
The present invention also is related to a process for manufacturing a substrate including: bringing the substrate into contact with a composition formed from organic assembling groups and from at least one precursor for the material constituting a mesoporous film; precipitating the precursor around the organic assembling groups and growing the molecules of the precursor; and then removing the organic assembling groups, wherein chemical molecules, such as hydrophobic/oleophobic molecules, are then brought into contact, in the form of a solution or of a gas containing them, with the mesoporous film. The composition has a pH, and prior to bringing the substrate into contact with the composition, a layer having an isoelectric potential greater than or equal to the pH of the composition may be deposited on the substrate. In some embodiments, the organic assembling groups are micelles of cationic surfactant molecules, the precursor is a silicon alkoxide, and the organic assembling groups and precursor are in solution and possibly in hydrolysed form. The cationic surfactant may be cetyltrimethylammonium bromide, the precursor may be in solution due to hydrolysis in an acid medium of Si(OH)4, and the surfactant/Si molar ratio may be between 10xe2x88x924 and 0.5.
The present invention further is related to a glazing for buildings or transportation vehicles that has a transparent surface, wherein at least a portion of the transparent surface includes a substrate coated with a mesoporous film and chemical molecules bonded thereto.
In addition, the present invention is related to a substrate including a coating surface and a mesoporous film having hydrophobic/oleophobic molecules bonded thereto, wherein the mesoporous film is disposed on said coating surface. The molecules include at least one of:
a) silicones; and
b) compounds satisfying the formulae xe2x80x83and Rpxe2x80x2SiX4-pxe2x80x2xe2x80x83xe2x80x83(II)
xe2x80x83wherein m=0 to 15, n=1 to 5, p=0, 1 or 2, R is a linear or branched alkyl group or a hydrogen atom, X is a hydrolysable group such a halogen, alkoxy, acetoxy, acyloxy, amino or NCO group, and pxe2x80x2=0, 1, 2 or 3. In some embodiments the mesoporous film has pores sized between about 1.2 nm and about 40 nm, and in other embodiments the pores are sized between about 1.2 nm and about 20 nm. The mesoporous film may be a periodic lattice including domains of at least 20 nm, and the mesoporous film may be formed of at least one compound including at least one of Si, W, Sb, Ti, Zr, Ta, V, Pb, Mg, Al, Mn, Co, Ni, Sn, Zn, and In. The coating surface may be at least one of glass, ceramic, glass-ceramic, or polymer.
The inventors have now employed a different technique, capable of increasing the durability of the hydrophobic/oleophobic coatings of the abovementioned types.
For this purpose the subject of the invention is a substrate coated with a mesoporous film characterized in that chemical molecules (especially hydrophobic/oleophobic molecules) are bonded to the mesoporous film.
Within the context of the invention, the term xe2x80x9cmesoporousxe2x80x9d refers to pores having a size of between 1.2 and 40 nm, in particular 1.2 and 20 nm. Specifically it has been found, not without surprise, that the grafting of hydrophobic/oleophobic molecules onto a messoporous layer guarantees that the hydrophobic/oleophobic function is remarkably persistent over time, even under severe erosion conditions. The excellent performance explained below is assumed to result from the combination of at least four characteristics:
1) good adhesion of the mesoporous coating to the substrate;
2) good adhesion, promoted by mechanical anchoring, of the hydrophobic/oleophobic molecules to the mesoporous coating;
3) good abrasion resistance of the mesoporous coating; and
4) release and activation, staggered over time, of the hydrophobic/oleophobic molecules.
The substrate may bexe2x80x94but is not necessarilyxe2x80x94transparent and has, in this case, excellent optical properties allowing it to meet the standards applicable to use in glazing.
Chemical molecules other than hydrophobic/oleophobic molecules may also be bonded to the mesoporous film so as to form coatings of excellent durability.
These are, in particular, hydrophilic/oleophilic molecules from which mention may be made, as final product or as precursor, of (meth)acrylic polyacids as they are or at least partially salified by sodium, potassium, caesium, etc., nonionic surfactants, cellulose esters, such as hydroxypropylcellulose, chitosan and chitin derivatives, polymethacrylates, polyvinyl alcohols and polyvinyl acetate, polypyrrole, polyaniline, polyacrylamide, poly(N,N-dimethylacrylamide), poly(N-isopropylacrylamide), polyethylene glycol, polypropylene glycol, polyoxyethylene having hydroxy or methoxy terminal functional groups, polyallylamine hydrochloride, polysaccharides, (branched) dextrans, pollulan (linear polysaccharide), poly(styrenecarboxylic acid) and salts thereof, poly(stryrenesulphonic acid), sodium polystyrene sulphonate, polyvinyl butyral, poly(2-vinyl-N-methyl pyridinium iodide), poly(4-vinyl-N-methyl pyridinium iodide), poly(2-vinylpyridine), poly(2-vinyl-pyridinium bromide), polyvinyl pyrrolidone, copolymers obtained from initial monomers of the various aforementioned polymers, and especially block copolymers, certain titanium compounds, such as tetraisopropyl or tetraisobutyl titanium compounds, possibly stabilized, for example by acetyl acetonate, titanium tetrachloride, etc.
It is also possible to bond to the mesoporous film anti-bacterial molecules, anti-fungal molecules, or molecules of conventional fragrances, etc.
The process of bonding them to the mesoporous film comprises, depending on the case in situ polymerization and/or impregnation.
The substrate preferably consists of a glass material or a plastic of the aforementioned type. It may consist of a single sheet or a laminate formed from several sheets joined together, or else it may be a solid object whose surface intended to receive the mesoporous coating is smooth and, in general, but not necessarily, flat.
The glass material in which the substrate can be formed is a glass, a ceramic or a glass-ceramic. It is preferred to employ glass, especially float glass of conventional composition, possibly hardened or toughened, an aluminium borosilicate and a sodium borosilicate or any other composition. In this case, the invention in no way excludes placing, between the film and the mesoporous film, or on that side of the glass sheet opposite the one bearing the mesoporous film, customary functional layers for glazing, namely anti-reflection multilayers or, on the contrary, reflecting layers, electrically conducting layers, decorative layers, or layers having thermal properties such as low emissivity, etc.
Many chemical elements may be at the basis of the mesoporous film. It comprises, as essential constituent material, at least one compound of at least one of the elements: Si, W, Sb, Ti, Zr, Ta, V, Pb, Mg, Al, Mn, Co, Ni, Sn, Zn.
With reference to the above description of the chemical molecules which, in accordance with the invention, may be bonded to the mesoporous film and which comprise certain titanium compounds as hydrophilic/oleophilic molecules, it should be noted that when the mesoporous film itself is based on titanium, especially in the form of the dioxide TiO2, it also exhibits hydrophilic/oleophilic (anti-misting/antifrosting) properties together with the ability to decompose organic residues (anti-staining property) photocatalytically, and this being in the absence of bonding with chemical molecules. However, the bonding to this type of mesoporous film of certain titanium compounds is capable of increasing to a greater or lesser extent durability of the abovementioned corresponding functions.
According to an advantageous characteristic, the mesoporous film has a periodic lattice on the scale of domains of at least 20 xcexcm. In other words, the mesoporous film comprises a multitude of identical geometrical features which are characterized by a dimension of at least 20 nm, but are oriented randomly. This characteristic dimension corresponds to a dimension of coherent diffraction domains and can be deduced, in a known manner from the Scherrer formula for the width of the main peakxe2x80x94indexed 100xe2x80x94of the X-ray diffraction diagram. The advantage of the periodicity on a relatively large scale of the mesoporous lattice is that it is possible to orient the porous domainsxe2x80x94corresponding to the abovementioned individual featuresxe2x80x94in an ordered manner, for example all perpendicular to the substrate or all parallel to the substrate, for the purpose, especially in the latter case, of obtaining electrically conducting coatings.
According to one particularly advantageous embodiment of the invention, the mesoporous film is electrically conducting. It then consists, for example, of substoechiometric and/or doped metal oxides as described in Application FR 2 695 117.
Examples mentioned in that application are tin-doped indium oxide (ITO), indium-doped zinc oxide (In:ZnO) fluorine-doped zinc oxide (F:ZnO), aluminum-doped zinc oxide (Al:ZnO) or tin-doped zinc oxide (Sn:ZnO) and fluorine-doped tin oxide (F:SnO2). In addition to their electrical conduction properties, these materials are described as having reflection properties in the infrared, especially low-emissivity properties. However, the capability of the mesoporous film to conduct electricity is, within the context of the present invention, aimed mainly at providing the antistatic function, that is to say the ability to dissipate electrostatic charges and to prevent them from building up locally and, to a lesser extent, the construction of heating films, especially for defrosting and demisting windows. Another electrically conducting material that can be used is antimony-doped tin oxide Sb:SnO2 (the antimony being pentavalent or trivalent).
The thickness of the mesoporous film on the substrate of the invention is advantageously between 10 nm and 10 xcexcm, and in particular between 0.05 and 5 xcexcm.
The hydrophobic/oleophobic molecules are preferably chosen from the group consisting of:
a) silicones and
b) compounds satisfying the formulae: xe2x80x83and Rpxe2x80x2SiX4-pxe2x80x2xe2x80x83xe2x80x83(II)
xe2x80x83in which:
m=0 to 15;
n=1 to 5;
pxe2x80x2=0, 1 or 2;
R is a linear or branched alkyl group or a hydrogen atom;
X is a hydrolysable group such as a halogen, alkoxy, acetoxy, acyloxy, amino or NCO group;
pxe2x80x2=0, 1, 2 or 3.
A standard compound satisfying formula (II) is octadecyltrichlorosilane.
As silicones, mention may be made of polydialkylsiloxanes. Compounds satisfying formula (I) have already been described elsewhere, for example in Application EP 0 799 873 A1.
Moreover, the subject of the invention is also a process for manufacturing a substrate as described above, in which:
the substrate is brought into contact with a composition formed from organic assembling groups and from at least one precursor for the material constituting the mesoporous film;
the precursor precipitates around the organic assembling groups and its molecules grow; and then
the organic assembling groups are removed, for example by calcining or extraction with acidified ethanol.
According to the invention, this process is characterized in that chemical molecules, such as hydrophobic/oleophobic molecules, are then brought into contact, in the form of a solution or a gas containing them, with the mesoporous film.
This process is remarkable in that it allows pores of approximately monodispersed size, of between 1.2 and 40 nm, to be easily obtained. This size can be adjusted by a suitable choice of the organic assembling groups, that is to say for example the greater or lesser length of the carbon chains constituting them. The durability of the hydrophobic/oleophobic function of the substrate, resulting from bringing the hydrophobic/oleophobic molecules into contact with the mesoporous film formed as indicated, is excellent.
Depending on the nature of the surface intended to be coated with the mesoporous film, it may be recommended, or even be necessary, to insert a primer layer so as to promote adhesion of the mesoporous film to its substrate and/or simply obtain a high enough quality of this adhesion. For this purpose, prior to the substrate being brought into contact with the composition containing the precursor for the mesoporous material, a layer having an isoelectric potential greater than or equal to the pH of the said composition is deposited on the substrate.
One particularly favourable method of implementing the process of the invention is one in which the organic assembling groups consist of micelles of cationic surfactant molecules, the precursor for the mesoporous material is a silicon alkoxide and they are in solution and, possibly, in hydrolysed form.
Particularly advantageously, the cationic surfactant is cetyltrimethylammonium bromide, the precursor for the mesoporous material is in solution in its form resulting from hydrolysis in acid medium, Si(OH)4, and the surfactant/Si molar ratio is between 10xe2x88x924 and 0.5. This combination constitutes a set of optimum conditions for obtaining the mesoporous film; it is assumed that this combination has a favourable influence on the micellar geometry, but this relies on complex energy modifications not completely understood at the present time.
However, one of the major advantages of the technique used to implement the invention is the possibility of varying the size of the pores of the mesoporous film within all the values indicated above by choosing the organic assembling groups judiciously. Thus, for these, anionic surfactants, nonionic surfactants, amphiphilic molecules, for example block copolymers, etc., may be used.
Another subject of the invention consists of glazing for buildings or transport vehicles, at least part of the transport surface of which consists of a substrate described above.
The example which follows will allow the invention to be more clearly understood.